1. Field of the Invention
The invention relates to a tapered roller bearing and a power transmission device.
2. Description of the Related Art
Tapered roller bearings have a larger load-carrying capacity and a higher stiffness than those of other kinds of equivalent-size rolling bearings. Therefore, tapered roller bearings are adopted in vehicle power transmission devices, such as a differential gear mechanism and a transaxle mechanism, which require bearings having a large load-carrying capacity and a high stiffness. FIG. 11 is a sectional view of a conventional tapered roller bearing, taken along its axial direction. As illustrated in FIG. 11, a tapered roller bearing 100 includes an inner ring 101, an outer ring 102, tapered rollers 103, and an annular cage 104. The tapered rollers 103 are rollably disposed between the inner ring 101 and the outer ring 102. The cage 104 holds the tapered rollers 103 at equal intervals in the circumferential direction. Each tapered roller 103 has a roller large end face 103a formed as a convex face. The inner ring 101 has a large rib end face 101a formed as a concave face. These configurations reduce the sliding friction between the two end faces 103a, 101a (see, for example, Japanese Utility Model Application Publication No. 5-75520).
For the tapered roller bearing 100, the degree of curvature radius of the roller large end face 103a of each tapered roller 103 and that of the large rib end face 101a of the inner ring 101 are not clearly determined. Therefore, if the curvature radius of each of the two end faces 103a, 101a is set to a certain value, it is not possible to reduce the sliding friction between the two end faces 103a, 101a in some cases.